1. Field of the Invention
The present invention relates to a recording medium playback apparatus for combination of a multiplicity of video signals, each corresponding to an H-line, reproduced through simultaneous playback of a plurality of recording mediums carrying different video signals.
2. Description of the Prior art
It is essential for recording and playing back a high definition TV signal, which is a data signal having a wide band of frequencies, into and from a recording medium, e.g. a video disk, to enhance the density of recording or increase the rotating speed of a spindle motor, whichever will handily be realized by the up-to-date techniques.
Such an improved method has been developed in which a high definition TV signal is frequency divided into a plurality of video signals which are then recorded onto a set of video disks and during playback, the video signals reproduced through playing back of the video disks with a plurality of players actuated simultaneously are combined together in H-lines for reproduction of a video image, as disclosed in Japanese Patent Laid-open No.63-175595.
FIG. 1 shows the waveform of three channel signals which are derived from a high definition TV signal and reproduced through playing back three video disks with three disk players. The three channel signals are then combined in H-lines for reproduction of a picture.
In this method, a jump to a desired frame can be carried out with fair smoothness by actuating one or two of the three players for specific playback operation, e.g. search or scanning, although a decrease in the quality of a reproduced image is inevitable more or less. Reproduced signals from the player(s) actuated in the specific playback mode are not appropriate for use. Thus, they have to be compensated using a normal signal from the remaining one or two players actuated in the normal playback mode. It is, however, known that when a target picture contains movement, compensation with a corresponding H-line of the preceding frame tends to result in drift of the preceding frame image. Accordingly, the compensation is preferably conducted using adjoining or adjacent line signals of the same frame.
Such a compensation circuit acts similarly to a dropout compensation circuit and, thus, will be appropriated for common use. This technique has been proposed by the Applicant of the present application, as disclosed in Japanese Patent Application 2-143594.
FIG. 2 is a block diagram showing such a common use application. As shown, DOS represents a dropout detection signal. (In this embodiment, a dropout is expressed by the logic state "0".) Also, DIS represents a disable signal indicating the disable state in which no normal video signal is available, e.g., a specific playback mode (and which is also expressed by the logic state "0"). DOS and DIS are supplied to an OR gate 33 which in turn delivers an output DO to a dropout compensation circuit 34.
FIG. 3 illustrates a common dropout compensation circuit. When DO is at logic "1", a switch 34b is turned to the side A and, thus, an input signal becomes an output signal directly. When DO is at logic "0", the switch 34b is shifted to the side B allowing an input signal for the preceding H-line from a 1 H-line delay circuit 34a to become an output signal. As understood, if dropout or disable state occurs in a row of two or more H-lines, compensation cannot be executed.
FIG. 4 shows an improved circuit for compensation with cyclic action, in which the input of the 1 H-line delay circuit 34a is connected to the output of the switch 34b. Accordingly, when a series of DOS for consecutive H-lines are at logic "0", a normal video signal of the preceding H-line is constantly fed in, allowing continuous compensation. However, the compensation circuit is intended to deliver a series of the same H-line signals thus causing vertical foldover to appear in a reproduced image which will thus decline in quality.
Particularly during a specific playback mode in which pickups on two of the three players are actuated for jump action, a couple of video signals for two consecutive H-lines will be absent more frequently. A problem is that the known compensation method using a normal H-line video signal cannot offset such absence.